The present invention is directed to an insulin delivery method and apparatus and in particular to a closed-loop system in which the body's requirements for insulin will be delivered as needed by the system on a continuous basis in the amounts required.
The normal functioning of the human body provides for extremely precise maintenance of various constituents of bodily fluids. This consistency is the result of the operation of several physiological mechanisms, including the negative-feedback system of the endocrine system. Physiologic events brought about by changes in the concentration of a given substance result in the restoration of the substance to its original concentration. For example, a rise in the blood sugar level causes an increase in the amount of insulin secreted by the pancreas. The resulting increase in the amount of circulating insulin affects many body tissues in a manner which causes a portion of the sugar to leave the circulating fluids to an extent which results in a restoration of the blood sugar level to its appropriate physiologic range. The decrease in blood sugar inhibits the further release of insulin, halting the removal of blood sugar from the system such that the re-established concentration is maintained.
In the healthy, non-diabetic individual, this closed loop system operates properly, and the blood sugar level varies little, except for a short period after meals when the blood sugar level increases. In the non-diabetic individual this increase is restricted in both magnitude and duration. In the patient with diabetes, however, this control is lost, and accordingly external mechanisms must be employed to control the blood sugar level.
In the past, such systems have been of the open loop variety, and are employed to introduce into the body a predetermined amount of insulin, irrespective of the precise needs of the body at that point in time. The dosage level may be determined by the consideration of a variety of generalized factors, including the age, weight and health of the individual, as well as other pertinent factors, but ultimately is an educated guess as to the patient's actual requirements.
Illustrative of such systems are those of U.S. Pat. No. 4,559,037 of Dec. 17, 1985 to Franetzki; U.S. Pat. No. 4,601,707 of July 22, 1986 to Albisser et al; and U.S. Pat. No. 4,398,908 of Aug. 16, 1983 to Siposs. None of these systems provides a mechanism by which actual insulin needs can be estimated and accordingly cannot provide the "fine tuning" of insulin delivery required for optimum body health.
In addition to the increase in blood sugar which rises after a meal blood circulation to and from the digestive tract similarly rises. Rather than the direct monitoring of blood sugar level, the present invention relies upon the sensing of digestive system blood flow to provide a means of real time sensing required for a closed loop insulin delivery system. As the circulation to and from the digestive system increases with food ingestion and decreases during stress reactions in a manner analogous to bodily insulin release, monitoring of this blood flow provides an acceptable basis around which an insulin delivery system can be designed.